Astrocytes respond to all forms of CNS insult by a process commonly referred as reactive astrogliosis characterized as hypertrophy of cellular processes and upregulation of intermediated filament proteins such as glial fibrillary acidic protein (GFAP). Compelling evidence has indicated that reactive astrogliosis is not simply an all-or-none phenomenon but, rather, a finely tuned continuum of molecular, cellular, and functional changes that range from subtle alternations in gene expression to scar formation. Recent research findings have also suggested that reactive astrogliosis may exert both beneficial and detrimental effects in a temporal dependent manner regulated by specific molecular signaling cascades. Increasing evidence has indicated that p38 plays a role in many other biological functions at the CNS. The activation of p38 signaling releases pro-inflammatory cytokines that are known to be involved in various CNS disorders including ischemic stroke, Alzheimer's disease, Parkinson's disease, multiple sclerosis, neuropathic pain and depression. The role of p38 MAPK in peripheral immune and inflammatory response has been extensive studied. However, the action of p38 in astrogliosis, the major component of neuroinflammatory response in CNS, has largely unknown. Our preliminary study demonstrated an activation of p38 signaling in reactive astrogliosis in the glial scar area in a mouse ischemic stroke model. Our laboratory has established a novel transgenic mouse line (hGFAP Cre/p38 loxP) in which the hGFAP promoter-driven Cre transgene deletes the floxed p38?ene and a downregulation of GFAP expression was found in primary astrocytes derived from the transgenic mice. Consistently, attenuation of reactive astrogliosis was observed upon p38 inhibition in primary astrocyte cultures. Reduction of ischemic stroke induced astrogliosis was observed in the hGFAP cre / p38 loxp mice as compared with wild type littermates. As Cre-mediated recombination is irreversible, embryonic expression in neural precursor cells directed by the GFAP promoter have resulted in substantial Cre-mediated recombination in mature neurons as well as glial cell in all GFAP-Cre mice characterized to date. In addition, the constitutive p38 knockout will not be able to study the role of p38 in astrogliosis in a temporal dependent manner. Therefore, there is a clear need of an inducible astrocyte specific p38 knockout mouse line. In this application, we proposed to establish an inducible astrocyte specific p38 knockout mouse line, characterize the inducible gene recombination and p38 knockout in the established transgenic mouse line, and determine the spatial and temporal dependent action of p38 knockout on glial scar formation and functional recovery after ischemic stroke. Specific Aim 1 is to establish the inducible astrocyte specific p38 knockout, hGFAP Cre-ERT2 / p38 loxP, mouse line. Specific Aim 2 is to determine the spatial and temporal dependent action of p38 knockout on glial scar formation and functional recovery after ischemic stroke using the established hGFAP Cre-ERT2 / p38 loxP mouse line. We predict that, in the established hGFAP Cre-ERT2 / p38 loxP mouse line, tamoxifen inducible gene recombination will be achieved predominantly in astrocyte with a minimal in the neural stem cell at subventricular zone. We expect that induction of p38 MAPK knockout in astrocyte after ischemic stroke attenuates glial scar formation, ameliorates the inhibitory action of glial scar on axonal sprouting and synaptogenesis, and enhances functional recovery.